Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $52.45   6.441%   $55.8283   $55.83   $55.85   $55.80  
  Purchase #2 $99.39   4.861%   $104.2213   $104.22   $104.20   $104.20  
  Purchase #3 $240.92   7.611%   $259.2564   $259.26   $259.25   $259.30  
  Purchase #4 $96.55   5.124%   $101.4972   $101.50   $101.50   $101.50  
  Purchase #5 $244.61   6.219%   $259.8223   $259.82   $259.80   $259.80  
  Purchase #6 $31.83   9.117%   $34.7319   $34.73   $34.75   $34.70  
  Purchase #7 $189.54   5.115%   $199.235   $199.24   $199.25   $199.20  
  7 purchase totals = $955.29       $1,014.5924   $1,014.60   $1,014.60   $1,014.50